The thermodynamic efficiency of power generating cycles depends on the maximum temperature of its working fluid which, in the case for example of a gas turbine, is the temperature of the hot gas exiting the combustor. The maximum feasible temperature of the hot gas is limited by combustion emissions as well as by the operating temperature limit of the parts in contact with this hot gas, and on the ability to cool these parts below the hot gas temperature. In particular blades, i.e. rotating blades and vanes (stationary blades), are exposed to high temperature combustion gases, and consequently are subject to high thermal stresses. Methods are known in the art for cooling the vanes and reducing the thermal stresses. Typically high pressure air, discharged from a compressor, is introduced into an interior of an air-cooled vane from a vane root portion. After cooling the vane the cooling gas is discharged from the vane into a hot gas flow path of the gas turbine.
The region of a vane where the airfoil is connected to the platform is highly loaded and often subject to additional stresses due to thermal mismatches and different thermal expansions of the airfoil and the platform. For a smooth transition and to reduce peaks in the stress distribution a rounded transition from platform to airfoil has been suggested. Such rounded transitions or connections are typically called fillet.
However cooling of fillets is difficult and requires additional cooling gas flow, which can lead to a reduction in power and efficiency.